1. Field of the Invention
The present invention pertains to a method of determining changes in position of subterranean or submarine pipelines due to subsidence or other causes by making measurements of the magnetic anomaly created by the pipeline with respect to the earth's magnetic field.
2. Background
Changes in position and the resultant stresses exerted on buried fluid transmission pipelines are of constant concern from an environmental, as well as economic, standpoint. In many parts of the world, fluid transmission pipelines may require burial in unstable strata or in submarine locations which are subject to strong currents, ice movement or impact by ships or their ground tackle. Relatively slight movements of fluid transmission pipelines in the range of from less than one foot up to several feet should be capable of recognition and monitoring to avoid eventual line rupture and the substantial economic loss and environmental damage which might be caused as a result thereof.
Various techniques for measuring change in curvature and other parameters indicating movement of a section of fluid transmission pipeline have been contemplated, including traversing the line with a pipeline pig having onboard a fully gimballed inertial guidance system, measurements with surveyor's levels or transits to determine height changes of surveying rods attached to the pipe, acoustic emission techniques and radar surveillance.
Although it has been suggested that measurements of the intensity of the earth's magnetic field can be made for determining approximate locations of buried objects such as transmission pipelines, methods and apparatus relying solely on measuring the earth's magnetic field intensity to determine the precise location of a pipeline with respect to any vertical or lateral changes in position have not, it is believed, heretofore been attempted or developed. It is to this end that the present invention is directed with an object to provide an improved system for monitoring vertical as well as lateral displacements of sections of fluid transmission pipelines in various subterranean locations.